One of the sources of that pollution, according to city officials: old septic tanks in nearby neighborhoods that leak or flood and allow human waste to flow into the creek, which empties into Clearwater Harbor.

Starting next year, the city will begin addressing the pollution problem by extending sanitary sewer service to almost 500 homes in the Idlewild neighborhood north of the creek.

The neighborhood in northwest Clearwater is bounded by Sunset Point Road to the south, Union Street to the north, Douglas Avenue to the west and Kings Highway to the east.

Septic tanks in the Idlewild neighborhood can be 60 years old, while the average life span of a septic tank is just 12 to 20 years, said Tracy Mercer, the city's public utilities director, adding that the tanks become less efficient as they age.

The $6.7 million project to extend sewer lines into the neighborhood will begin in spring 2013 and run until 2015. The work will include stormwater drain improvements along several streets.

Connecting to the sewer system won't be cheap for residents of the middle-income neighborhood.

Owners of the 496 homes affected by the project will have to pay a $900 one-time impact fee to connect to sewer. If they connect during the construction period, that's all they will have to pay — the city will pick up the connection fee and septic tank abandonment fee, which can total as much as $2,800.

Those who decide to connect within a year of the completion of construction will pay the $900 impact fee and the connection and tank abandonment fees, minus a $450 credit.

Property owners who wait longer than a year after construction will be responsible for all fees when they connect.

The project area includes properties inside the city limits and in unincorporated Pinellas. Property owners outside the city will have to agree to annex into the city to connect to the service.

Those with working septic tanks will not be forced to connect, but will later have to pay a monthly sewer availability fee even if they aren't connected to the sewer lines.

Having a septic tank isn't without costs, city officials point out. The untreated sewage in the tanks can overflow and damage property. The tanks need to be replaced from time to time. And they are known contributors to polluted groundwater and fouled waterways.

The 496 homes in Idlewild represent just over 10 percent of the 4,229 homes in Clearwater's water service area that are still using septic tanks, Mercer said. The city's goal, she said, is to switch the remaining homes over to the city sanitary sewer system within 20 years.